Formula One racing driver Michael Schumacher is said to be having "moments of consciousness and awakening" after more than three months in a coma.

The 45-year-old German suffered severe head injuries after a skiing fall at the end of December, and is being treated in a French hospital.

Doctors who have been trying to bring Schumacher out of the coma, were reported to have said last month that "only a miracle" would lead to his recovery.

In an unexpected statement on Friday, Sabine Kehm, the family's spokesperson, sounded the most optimistic note since Schumacher's accident in the French alpine ski resort of Meribel.

"Michael is making progress on his way [sic]. He shows moments of consciousness and awakening. We are on his side during his long and difficult fight, together with the team of the hospital in Grenoble, and we remain confident," she said.

"We would like to thank you all for the continuous sympathies. At the same time, we again ask for understanding that we do not intend to disclose details. This is necessary to protect the privacy of Michael and his family, and to enable the medical team to work in full calmness."

Head injury specialists urged caution, saying at this stage of treatment it is difficult to distinguish real patient consciousness from physical reflexes.

Schumacher was skiing in a narrow off piste area between two marked pistes with his son and a group of friends when he fell. French investigators say the seven-time world champion, an experienced skier, was not going fast and was trying to slow when he fell and hit his head on a rock. The force of the impact broke his helmet in two.

Doctors put him in a coma to ease the pressure on his brain. They have been reducing the sedatives in an attempt to wake him since the end of January.

Medical experts say patients undergoing the long process of waking from a coma often have "sleep-wake cycles" and can make physical movements and noises. However, it is hard to establish if the patient is conscious of what they are doing.

Peter Hutchinson, professor of neurosurgery at Cambridge University and chief medical officer for the British Grand Prix, said: "He could be opening his eyes, but the critical sign is whether he can obey commands. We have a young girl on the ward at the moment who has been under around the same time as Schumacher. She opens her eyes, but she is not there."

Hutchinson added: "In any case it's very difficult to give any sort of prognosis within the first six months. In my mind the statement implies that he has his eyes open, but not a lot more than that. I don't think it tells us very much.

"My feeling about this is that at this stage, things are not looking good."

Luke Griggs, spokesperson for the brain injury charity Headway, also urged caution and said the statement from Schumacher's agent "raises more questions than it answers".

"We know of patients who have defied doctors' predictions to make a reasonable recovery following periods of coma, but the longer a person is in a coma, the less likely it is that they will go on to make a full recovery," said Griggs.

"We would be very cautious about people being too enthusiastic about this statement. Of course, we are looking on very much from the outside, but if someone has been in a state of reduced consciousness for more than three months, the chances of them making a full, long-term recovery are not good."

He added: "We were surprised that this statement was made and rather confused by it. We are treating it with a good deal of caution.

Hutchinson said it was crucial to know if Schumacher was still being sedated and regretted more details about his medical condition were not being released.

"It's desperately sad what has happened to him, but he is a public figure and a lot of people would like to know a bit more about how he is.

"It's difficult to say if this is encouraging. We would have to know how he was a month ago to be able to say if there was any improvement."